Disorders of the hip include coxitis, dislocations, fractures, and bursitis.
Coxitis
Coxitis is inflammation of the hip and may lead to osteoarthritis of the hip joint. Most cases are caused by trauma, such as a fall. Hip bone (pelvic) fractures and infections, particularly septicemia in young animals, may also be causes. Regardless of cause, the development of secondary osteoarthritis of the hip joint is common and leads to permanent lameness.
Lameness may be seen in both the supporting and the swinging leg. In severe cases, the horse may carry the leg. In less severe cases, the horse develops a rolling gait, elevating the affected quarter during weight-bearing and advancing the limb in a semicircular manner with a shortened forward stride. The toe may be worn from dragging. The horse often stands with the limb partially bent, the stifle turned out, and the point of the hock turned inward. The muscles of the hind quarter waste away due to disuse in longterm cases. X-rays of the joint may confirm the diagnosis but good images may be difficult to obtain in a large horse. Bone scans using nuclear scintigraphy are often used to identify the site of injury.
The outlook for recovery is poor. Treatment involves rest, and steroids injected into the joint may relieve the lameness temporarily in milder cases. Anti-inflammatory drugs are useful, but many horses are in too much pain for the drug to have a beneficial effect.
Dislocation of the Hip
The hip can dislocate when ligaments or joint membranes are ruptured due to trauma; however dislocation of the hip is uncommon in horses. When dislocation does occur, fracture of the hip bone or “locking” of the kneecap in an extended position often accompanies it.
When the round ligament of the hip joint ruptures, the stifle and toe of the hindlimb visibly rotate outward, while the hock rotates inward. The hip joint does not always completely dislocate, but when it does the gait is obviously affected. The thighbone rotates outward, and the horse resists bearing weight on that leg.
Relocation of the hip joint may be attempted under general anesthesia, but the longterm outlook for recovery is usually poor.
Pelvic Fracture
A horse may fracture its pelvis at any age, but the injury is most common in horses 6 months to 2 years old. Almost any part of the pelvic girdle may be involved. The outlook for recovery depends on the specific location of the injury and the extent of soft-tissue damage. A pelvic fracture can usually be confirmed by a veterinarian after a rectal examination, especially if the fragments are displaced. Considerable pain and lameness in the hindlimbs immediately follow the injury. If the lameness is not too severe, but a fracture is suspected, it is better to rest the horse for 4 to 6 weeks before giving a general anesthetic to do x-rays.
In more longterm cases, the lameness produces a wasting away of the gluteal muscles. X-rays can aid the diagnosis. Depending on the site of the fracture, there may be a hopeful outlook for recovery, particularly in young horses. Rest (for as long as 9 to 12 months) is usually the only treatment necessary. However, some pelvic fractures have a much more guarded outlook for recovery.
Trochanteric Bursitis (“Whirlbone” Lameness)
In trochanteric bursitis, inflammation of the bursa beneath the tendon of the middle gluteal muscle as it passes over the greater trochanter of the femur is the cause of discomfort and lameness. There is no whirlbone (or "whorlbone") in horses. It is most common in racing and sport horses, in which bursitis and soreness of the hindquarter muscles occur secondary to hock problems that alter the horse's normal gait and cause strain.
The bursitis causes shifts of weightbearing to the middle wall of the foot, wearing it down more than the outer side wall. The stride of the affected leg is shorter, and the leg rotates inward. The horse tends to carry its hindquarters toward the sound side. In longterm cases, the muscles of the hindquarters waste away, giving them a flat appearance. Pressure applied to the trochanter (the joint of the hip and thigh) will cause pain.
If the inflammation is severe, the horse should be rested and hot packs applied to the affected area. Injection of corticosteroids and hyaluronic acid (a component of synovial fluid) into the bursa temporarily relieves the inflammation. Addressing the primary problem, in the hocks is important to resolve this condition.
